As to burning wood for electric power production, this almost has to mean burning fiber which cannot be sold for a higher price. Trees (logs) which can be sawed into lumber, if there is a market for the lumber, or which can produce pulp for paper, or even stove wood for residential or small commercial use, produce much higher value than burning the trees in a power plant. A power plant has to compete in the market for its fiber fuel, and even at current depressed prices for fiber, the price still is too high to buy the trees for burning to produce electricity. And just about as soon as the price might drop low enough, the added demand by power plants will start to push the price back up again.
In short, brush, tops, branches, unmerchantable thinings and other round wood, deadwood are the likely target for a power plant. In our area these items barely produce a bid at a timber sale, and this stuff is "sold" mostly to prepare the harvested area for replanting, as otherwise it often needs to be piled in large slash piles and burned in the open air. Some slash, if left on the ground, attracts insect and other pests which are harmful to other living trees. There is controversy about how much of this can be taken out of the woods and for how long and still leave sufficient biomass on the forest floor to produce long term sustainable forests. Considerable research is continuing in this area.
The quantity of sustainable fiber available for power plants is an interesting question. Quantity is inextricably related to the price the power plant will pay, and currently that price is little if any more than the cost of chipping if needed, gathering and trucking the material to the plant. The forestry certification agencies have pretty good standards to insure long term, sustainable forests, and the great bulk of public (and much private) forest lands in MN are certified and audited. In Minnesota, forestry plans for the national forests, Minnesota state forests, and county public land forests are prepared and administered for long term healthy, sustainable forests, not only for fiber but also for clean water, wildlife habitat, and recreational uses. The current issues revolve around whether these plans are too conservative (harvest levels substantially below sustainable yields) and getting rid of unmerchantable, excess fiber, even if it has to be given away.
I think this issue is not settled, but paranoia on one side of the other is not helpful. Keep in mind that there has been little controversy over cutting forests for paper pulp or lumber, both high value products. Cutting forests for electric power production will have to compete in this larger market, and energy costs will have to go much, much higher to make it profitable to cut forests for electric power production.